194. ANNUAL REPORT SMITHSONIAN INSTITUTION, 1946 
citizens. Miniature films permit the detection of most such lesions. 
About 1 percent of apparently healthy adults are found to have some 
significant lung condition on such surveys, but fortunately only 1 
in 400 has evidence of “open” disease. 
The X-ray unit has not made the stethoscope obsolete but it has 
given the physician a weapon with which he may detect numerous 
diseases of the chest at a stage long before they could otherwise be 
discovered. In this manner they have been a major factor in saving 
countless lives and in preventing much advanced disease. 
LOCALIZATION OF FOREIGN BODIES 
X-rays are essential for the detection and accurate localization of 
most foreign bodies in the tissues. These bodies may be divided into 
two general types, nonopaque to the X-rays and opaque. Surprising 
as it seems, nonopaque foreign bodies frequently may be localized, 
with considerable accuracy, by careful examination. For example, 
a peanut lodged in one of the bronchial tubes will itself cast no 
shadow; however, it will produce partial or complete obstruction of 
the bronchus. As a result the involved lobe of the lung will show 
either persistent distention with air on expiration, or gradual col- 
lapse. Nonopaque foreign bodies in the alimentary tract often may 
be located by giving the patient small barium-soaked cotton pledgets 
or swallows of barium cream. Nonopaque foreign bodies in other 
parts of the body sometimes are located by injecting radiopaque 
liquids into draining sinus tracts. 
Opaque foreign bodies, common in war time, may be found and 
localized by various methods. The simplest is by roentgenoscopic 
and roentgenographic examination in two planes at right angles to 
each other. Other methods include parallax and triangulation. The 
detection and localization of small metallic bodies in the eye may be 
performed with the aid of special apparatus. That most generally 
employed involves examining the patient’s eye in accurate relation- 
ship to two fixed objects placed at a known distance from the cornea. 
The data obtained from two films made at different angles are trans- 
ferred to a special ruled chart, and the position of the body indicated 
in three different planes with an accuracy of less than one millimeter. 
Protection against unnnecessary or excessive exposure to X or ra- 
dium rays is one of the utmost importance for patient, operating per- 
sonnel, and radiologist. Protection against excessive exposure from 
the direct beam is now well established in responsible offices and de- 
partments by methods which include careful calibration of the ap- 
paratus, adequate distance between tube and patient’s skin, use of 
lead-protected shockproof tubes, suitable diaphragms, and filters. 
Protection against radiation scattered from the patient or the X-ray 
